Ovulation

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Ovulation
Fertilization
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Maturation of sperm

• Sperms
• Incapable of fertilizing the oocyte immediately
  after being released into the lumen of the
  seminefrous tubules
• Maturation
• In epidydimus

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• Epidydimus
• Fluid reabsorption
• Increase concentrations of sperm by 100 folds
• Estrogen dependent
• Quiescence of sperms
• Slow activity
• Movement depends on musculature
• Addition of chemicals
• Glycoproteins
• Coating of sperm surface

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• Maturation of sperm
• Ability to move on its own
• Nuclear condensation and loss of cytoplasm
• Metabolism alteration
• External source
• Increased mobility
• Changes in cell membrane
• Increased charge (glycosylation)
• Changes in protein profile
• Changes in lipid composition (fluidity)

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• Maturation of sperm
• Androgen dependent
• Very high concentrations (ABP)
• Conversion to DHT
• Increased bioactivity
• Entire process will take several months to few
  days

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Movement of sperms

• Entering vas deference from epidydimus
• Muscular contraction rather than fluid movement
• Dense mass
• Serve as reservoir of sperms
• Lost in urine if no ejaculation

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Sperm in male reproductive tract

• Semen
• Sperm plus seminal plasma
• Seminal plasma
• Derived from accessory sex glands
• Serves as fluid vesicle for transport
• Unnecessary for sperm function

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• Seminal plasma
• Derived from accessory sex glands
• Serves as fluid vesicle for transport
• Serves as buffer
• Basic in nature
• Neutralizes acids
• Provides nutrients
• Fluctose
• sorbitol

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• Semen composition
• Immune cells
• Infectious agents

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Deposition of semen into the female reproductive
tract

• Coitus
• Physiological changes
• Genitalia
• Other parts of body
• Phases
• Described in humans by Johnson and Masters
• Four phases
• Excitement (sexual arousal)
• Plateau (intense arousal)
• Orgasm (involuntary climax)
• Resolution
• Absolute refractory phase in male
• Immediately after orgasm

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• Excitement
• Vasocongestion
• Penile erection (engorgement of corpora cavanosa
  and corpus spongiosum)
• Vaginal lubrication (transudation)
• Enlargement of labia minora and clitorus
• Vaginal expansion
• Tenting effect on uterus
• Upward movement of uterus and cervix
• Fibrilation of uterus (contraction)
• Sex flush
• Myotonia
• Increased muscle tension

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• Plateau
• Increased testis size
• Elevated from the original position
• Secretion of fluid
• Cowpers gland
• Sex flushes
• Engorgement of vaginal wall
• Orgasmic platform
• Formation of seminal pool

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• Female orgasm
• Rhythmic contraction
• Vaginal wall
• Uterus
• Involuntary muscle spasm

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• Male orgasm
• Contraction of accessory sex gland
• Collection of semen into the urethral bulb
• Contraction of bladder muscle
• Emission stage of ejaculation
• Expulsion of semen/ejaculation
• Muscle contraction
• Reproductive tract contraction

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• Resolution
• Returning of body to nonaroused state
• Size of genitals
• Uptake of sperm by the cervix
• Dipping into the seminal pool as the uterus
  returns to the normal position
• Opening of cervical canal

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• Site of semen deposition
• Varies among species
• Humans and cattle
• Near external portion of cervix (cervical os)
• Uterus in other species
• Formation of plug
• Enzymatic reaction
• Prevent backflow of semen
• Buffers
• Prevent sperm from other males to fertilize eggs?

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Transport of sperm to the oviduct

• Sperm must enter female reproductive tract and
  reside there for some time
• Maximum fertility
• Sperm
• Viable inside of reproductive tract
• 24 to 48 hours in human
• 30 to 48 hours in cows
• Oocyte
• A finite life span
• 6 to 24 hours after ovulation in human
• Sperm must reach the oviduct at appropriate time
  in order to remain viable and fertile

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Transport of sperm to the oviduct
Preovulatry follicle
Semen pool

• Semen
• Deposited in the anterior part of the vagina near
  the cervix
• The majority of the sperm
• Lost because of retrograde flow of the mucus out
  of the vagina
• Killed because of the unfavorable environment for
  sperm survival in the vagina.

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Transport of sperm to the oviduct

• Some of the sperm
• Transported through cervical canal into the
  uterus within minutes after sperm deposition
• Rapid transport
• Rapid transport of sperm is caused by the
  contraction of myometrium (muscle layer of the
  uterus) and not by active movement of sperm
• Sperm that enter the oviduct by rapid transport
• Often non-viable and unlikely to participate in
  fertilization.

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Transport of sperm to the oviduct

• Many sperm
• Trapped in the folds and crypts of the cervix
• Formation of sperm reservoirs within the cervix
• Critical
• More sperm ultimately reach the oviduct when more
  sperm are available in the cervical reservoir

Folds and crypts of the cervix
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Transport of sperm to the oviduct

• Slow transport of sperm
• After establishment of reservoir
• Ensures the availability of sperm in the oviduct
  continuously
• Large number of sperms
• Fails to reach the oviduct
• Many obstacles such as folding of the uterine
  endometrium and the narrow diameter of the
  uterotubal junction
• Presumably to prevent polyspermy (more than one
  sperm fertilizing the oocyte)

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Transport of sperm to the oviduct
Uterotubal Junction
Ampullary- isthmic Junction
Isthmus
Ampulla
Infundibulum

• Aggregation of sperms
• The isthmus
• Sperm remain in the isthmus until ovulation
• Hyperactivation
• Rapid movement of tail and erratic swimming
  motion
• Near ovulation
• Essential for their upward movement toward the
  ampulla.

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Transport of sperm to the oviduct
Uterotubal Junction
Ampullary- isthmic Junction
Isthmus
Ampulla
Infundibulum

• Capacitation
• Changes in cell surface of the sperm
• Required for proper attachment and penetration of
  the zona pellucida when the sperm encounters the
  oocyte

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• Capacitated sperms
• Acrosome reaction when encountering the oocyte
• Ability to bind and penetrate zona pellucida
• Swelling of acrosome
• Fusion of acrosomal membrane
• Exocytosis of acrosomal content
• Ca and cAMP dependent

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• Acrosome reaction
• Triggered by the protein in the zona pellucida
• ZP3
• Sperms have receptors for ZPs
• Increased Ca uptake
• Release of hexosaminidase B (removal of ZP3)

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• Acrosome reaction
• Must take place near the oocyte
• Reduced sperm viability

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Fertilization

• Sperm encountering the oocyte
• Migration through the remaining cumulus cells
  that surround the oocyte
• Sperm binds to the zona pellucida
• Mediated by the sperm binding sites present on
  zona pellucida

Cumulus cells
First polar body
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Fertilization

• Within minutes of binding, the sperm begins to
  penetrate the zona pellucida, and eventually
  fuses with the oocyte
• Equatorial and postacrosomal region
• Ca-dependent reaction
• Immediately after the sperm fuses with the
  oocyte, the oocyte extrudes the second polar body
• Oocyte becomes a haploid cell

Zona pellucida
Second polar body
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Fertilization

• Once a sperm fuses with the oocyte, the zona
  pellucida becomes hardened
• Release of Ca
• Sperm binding sites disappear from the zona
  pellucida
• Hardening of zona and loss of sperm binding sites
  are necessary in order to prevent polyspermy

Head of sperm
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Fertilization

• Membrane of the sperm head
• Degraded and replaced by a new membrane
• Formation of a structure called the male
  pronucleus
• The maternal half of chromosomes
• The female pronucleus.

Male pronucleus
Female pronucleus
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Fertilization

• Male and female pronuclei move toward the center
  of the oocyte
• Degradation of the membrane that surrounds each
  pronucleus
• Mixing of maternal and paternal chromosomes
• Restoration of the total number of chromosomes

Zygote